164 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



and the fibres that they give off, are very strong. We 

 have already noted the presence of small pebbles in 

 the gizzard ; the duty of these is to act as grinding 

 stones. On the contraction of the muscles the cavity 



B 



Fig. 73. Horizontal Sections of the Gizzard of a Goose, in contraction 

 (A) and relaxation (B). (After Garrod ; Proceedings of the Zoolo- 

 gical Society, 1872, page 527.) 



of the gizzard is, of course, diminished in extent, and 

 the food contained in it crushed against the stones. 

 It sometimes happens that the lower end of one pad 

 and the upper end of the other are respectively better 

 developed than the rest ; when this happens a slight 

 sliding is added to the crushing movement, which 

 must have considerable influence in breaking hard 

 grains. 



